kennycrudup

It's just a calculated guess, but I get on the app (or website) and try to buy a seat for the city pairs I'm interested in. If it shows "Sold Out" less than ~8hrs before the flight is due to leave I'll give up on that particular one unless I'm suddenly desperate to get there (even if a seat or two comes up the odds are A-List(+) SB aren't getting it; see the "A-list SB thread". If WGA is still available, that's good (as those fares come from early-availability buckets and either sell out first, or get repushed if sales are weak). Then as long as I don't see "only X seats left" on AT/BS that also seems to be a good sign.

Also, it's important to use the app/website to do "flight status" on the flights one or two back from your "target" flight- if they've been delayed so much they'll get in later or close to the one afterwards, a lot of people already in the airport will try to get on that (and have standby over everyone, IIRC).

ETA: and you have to keep checking, and make a judgement call to decide what flight will work for you; most times I'm leaving work early for this and have to factor in the time in traffic, so it's somewhat important to me to get it right so I don't waste valuable time I could be billing, only to end up watching Hulu in the airport as I wait for a seat.